Electrical conduit is typically used to support runs of electrical wires or cables. These conduits in certain instances are required to be grounded and which may be subject to movement relative to each other. Such relative movement requires the use of expansion-deflection type couplings to prevent damage to the conduit or the cables inside. Conduits supporting such electrical wires or cables may be interconnected by electrical fitting joints. Certain of these joints provide for thermal expansion, permitting relative movement between the conduits in response to ambient temperature fluctuations. These joints must not only provide for relative movement between the conduits, but also must maintain ground continuity across the conduits during such movement. Expansion-deflection type couplings are also necessary to provide the flexibility to accommodate such movement. Thus, expansion-deflection type couplings will allow for expansion, contraction and deflection caused by the relative movements as discussed above.
Examples of such expansion-deflection type couplings are shown in U.S. Pat. Nos. 2,885,461; 3,783,431 and 4,109,097.
U.S. Pat. No. 2,885,461 shows an expansion and deflection conduit coupling made of two end sleeves yieldingly connected in spaced apart end to end relation by a surrounding flexible elastic sleeve or tube made of plastic. Such a coupling will allow for expansion, contraction and deflection of the conduit without damaging the conduit and providing the necessary electric continuity.
U.S. Pat. No. 3,783,431 shows an electric connector with a tubular contact member having two universal joints mounting on the contact members to permit angular movement of the contact members relative to each other. A longitudinal movement of the contact member is caused by sliding a rod contact within the tubular contact. Furthermore, a tubular sheath of flexible material encircles a portion of the rod contact outside the tubular contact to weaken any ice forming thereabout to maintain the free movement inside the connector.
U.S. Pat. No. 4,109,097 shows an expansion-deflection coupling comprised of two independent hubs adapted to be threaded on the ends of opposed spaced apart conduits, a flexible grounding strap is connected completely within and between the hubs and a flexible watertight jacket is secured to the outer surface of the hub. Such a coupling allows for linear misalignment of the hubs up to ¾ of a inch and/or angular displacement of the hubs relative to each other up to 30° and also allows for expansion or contraction of the coupling up to ¾ of an inch.
The expansion-deflection couplings as discussed above in the prior art use an internal plastic sleeve to maintain constant inner diameter in any position and provide a smooth wire way for protection of wire insulation. Such couplings have very limited flexibility in expansion or contraction, in angular deflection and further in line or misalignment.
It is desirable therefore to provide an expansion-deflection coupling which will have more flexibility in axial expansion, and compression and angular deflection while providing protection to the wires or cables it contains.